Many members of Congress continue to grapple with the nuclear deal with Iran — and so do we. Like us, the undecideds see its benefits: The deal would block the uranium enrichment, plutonium separation and covert paths to a nuclear bomb for the next 15 years. Compared with today, with an Iran that is three months from break-out capability and with a stockpile of 10 bombs’ worth of low-enriched uranium, there can be little doubt that a deal leaves us far better off , producing a one-year break-out time and permitting the Iranians less than one bomb’s worth of material for the next 15 years . We also don’t believe that if Congress blocks the deal, a better one is going to be negotiated. Will the other members of the P5+1 be ready to return to the table because Congress says no? Will they even know who defines the U.S. position and what it is? We doubt it.

So if the deal, known as the Joint Comprehensive Plan of Action (JCPOA), has clear benefits and there is no obvious negotiated alternative , why are we still undecided? Put simply, because the deal places no limits on how much the Iranians can build or expand their nuclear infrastructure after 15 years. Even the monitoring provisions that would continue beyond 15 years may prove insufficient as the Iranian nuclear program grows. And Iran’s ability to dramatically increase its output of enriched material after year 15 would be significant, as Iran deploys five advanced models of centrifuges starting in year 10 of the agreement.

In terms of the size of its nuclear program, Iran will be treated like Japan or the Netherlands — but Iran is not Japan or the Netherlands when it comes to its behavior. It is, after all, one of three countries designated by the United States as a state sponsor of terrorism. Perhaps in 15 years we will see a very different Iran — not a sponsor of terrorism, not a threat to its neighbors, not led by those who declare that Israel, another U.N.-member state, should be eliminated. But, while we hope that Iran may change, we cannot count on it.

The fact that President Obama emphasizes that the plan depends on verification — not trust — also means that he is not assuming Iran will change. But verification means only that we can catch the Iranians if they cheat; what matters even more is that the Iranians recognize that they will pay a meaningful price when we catch them.

Read the article in full at the Washington Post.